Question

Congenital deafness in humans is due to the homozygous condition of either of the recessive genes d or e, or both of these genes. Both dominant D and E are necessary for normal hearing. Gene D/d affects the middle ear, while gene E/e affects the inner ear as indicated by E It does not matter how good the normal inner ear is: if there is something wrong in the middle ear, the individual is unable to hear. The same applies for the other gene. Give the phenotypic results of the following crosses: c) ddEE x DD eed) Dd EE x Dd ee

Answer 1

To make the punnet's square first we need to combine the allele to obtain the gametes possibilities. Then we make the cross to obtain the possible offspring

1 DdEE x 2 Ddee

Gametes:

1: DE / DE / dE / dE

2: De / De / de / de

Now we obtain the phenotypic ratios:

Given that dd/ee = deafness then:

4/16 of the offspring will have congenital deafness because of the genotype: ddEe specifically because of the dd alleles.